Imaging lens

ABSTRACT

There is provided a compact imaging lens which meets demand of low-profileness, reduction in telephoto ratio and low F-number, and properly corrects aberrations. An imaging lens comprising in order from an object side to an image side, a first lens, a second lens, a third lens, a fourth lens having a convex surface facing the image side near an optical axis, and a fifth lens having positive refractive power, wherein a below conditional expression (1) is satisfied: 
       0.64&lt; TTL/f &lt;1.0  (1)
     where   f: focal length of the overall optical system of the imaging lens, and   TTL: distance along the optical axis from an object-side surface of the first lens to an image plane.

The present application is based on and claims priority of Japanesepatent application No. 2017-008799 filed on Jan. 20, 2017, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an imaging lens which forms an image ofan object on a solid-state image sensor such as a CCD sensor or a C-MOSsensor used in a compact imaging device, and more particularly to animaging lens which is built in an imaging device mounted in anincreasingly compact and low-profile smartphone and mobile phone, aninformation equipment such as a PDA (Personal Digital Assistant), a gameconsole, PC and a robot, and moreover, a home appliance and anautomobile with camera function.

Description of the Related Art

In recent years, it becomes common that camera function is mounted inmuch information equipment. Furthermore, it becomes indispensable as anadditional value of the product to mount a camera in the mobile phoneand the smartphone, and the terminal equipment as the PDA. Not only themobile terminal equipment, but demand of products such as a wearableappliance, the game console, the PC, the home appliance and a drone withthe camera function is more increased, and development of products willbe rapidly made accordingly.

Corresponding to such image sensor which is compact and increases in thenumber of pixels, the imaging lens is also required to have highperformance in resolution and image quality, and therefore spreadthereof and reduction in cost are also requested.

In order to meet demand of high performance, the imaging lens comprisinga plurality of lenses becomes popular. There is also proposed theimaging lens comprising five lenses which may enable high performance tobe achieved more than that comprising three or four lenses.

As a conventional imaging lens comprising five lenses, for example, animaging lens disclosed in the following Patent Document 1 is known.

Patent Document 1 (U.S. Pat. No. 8,395,851) discloses an imaging lenscomprising, in order from an object side, a first lens having positiverefractive power, an aperture stop, a second lens having negativerefractive power, a third lens having convex surfaces facing the objectside and an image side, a fourth lens having a meniscus shape having aconcave surface facing the object side, and a fifth lens having aconcave surface facing the image side. Thus configured, the imaging lensaims high performance.

SUMMARY OF THE INVENTION

The imaging lens disclosed in the above Patent Document 1 is a lenssystem comprising a small number of lenses such as five, having a largediameter, being compact and being in high performance, and the lenssystem is configured to largely reduce manufacturing cost. This lenssystem certainly achieves brightness of F2.6. The lens configuration ofthe Patent Document 1, however has a problem that a ratio of total tracklength to focal length of an overall optical system becomes too large.Furthermore, when low-profileness and further low F-number are achieved,it is very difficult to correct aberration at peripheral area, andexcellent optical performance required in recent years are not obtained.

The present invention has been made in view of the above problems, andan object of the present invention is to provide an imaging lens whichsatisfies in well balance demand of a small size, low-profileness, andlow F-value applicable to the above mobile terminal equipment andinformation equipment, has a small ratio of a total track length to afocal length of an overall optical system to reduce telephoto ratio, andexcellently corrects aberrations and has high resolution.

Regarding terms used in the present invention, unless otherwise noted, aconvex surface or a concave surface of the lens implies a shape near theoptical axis (paraxial portion). The pole point implies an off-axialpoint on an aspheric surface at which a tangential plane intersects theoptical axis perpendicularly. The total track length is defined as adistance along the optical axis from an object-side surface of anoptical element arranged closest to the object side to the image plane.When measurement of total track length is made, thickness of an IR cutfilter or a cover glass which does not contribute to convergence anddivergence effect of light is regarded as an air.

An imaging lens according to the present invention is configured to forman image of an object on a solid-state image sensor, and comprises, inorder from an object side to an image side, a first lens, a second lens,a third lens, a fourth lens having a convex surface facing the imageside near an optical axis, and a fifth lens having positive refractivepower, wherein a below conditional expression (1) is satisfied:

0.64<TTL/f<1.0  (1)

wheref: focal length of an overall optical system of an imaging lens, andTTL: distance along the optical axis from an object-side surface of thefirst lens to an image plane.

The imaging lens having the above configuration achieves thelow-profileness by increasing the refractive power of the first lens,and corrects in well balance aberrations such as spherical aberration,astigmatism, field curvature and distortion using the second lens andthe third lens while maintaining the low-profileness. The fourth lenshas a convex surface facing the image side near the optical axis, andgently guides light rays diffused at the second lens to the fifth lensby facing the convex surface to the image side and excellently correctsoff-axial aberration. By having the positive refractive power, the fifthlens suppresses an incident angle of peripheral light ray provided tothe image sensor. Therefore, a lens diameter of the fifth lens can besmall and reduction of the diameter of the imaging lens is achieved.

The conditional expression (1) defines the distance along the opticalaxis from the object-side surface of the first lens to the image planeagainst the focal length of the overall optical system of the imaginglens, and is a condition for achieving shortening of the total tracklength. When the value is below the upper limit of the conditionalexpression (1), total length can be shortened and it becomes easy toachieve a compact size. On the other hand, when the value is above thelower limit of the conditional expression (1), it becomes easy tocorrect the field curvature and axial chromatic aberration, andexcellent optical performance can be maintained.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (2):

f<5.8  (2)

wheref: focal length of an overall optical system of an imaging lens.

The conditional expression (2) defines the focal length of the overalloptical system, and by satisfying the conditional expression, an opticalsystem having a shorter total length is provided.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (3):

0.31<f1/f<0.63  (3)

wheref1: focal length of a first lens, andf: focal length of an overall optical system of an imaging lens.

The conditional expression (3) defines refractive power of the firstlens, and is a condition for shortening the total length and excellentlycorrecting the aberration. When the value is below the upper limit ofthe conditional expression (3), it becomes easy to make the total lengthshort while maintaining the refractive power of the first lens. On theother hand, when the value is above the lower limit of the conditionalexpression (3), it becomes easy to suppress high-order sphericalaberration and coma aberration.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (4):

−0.85<f2/f<−0.36  (4)

wheref2: focal length of a second lens, andf: focal length of an overall optical system of an imaging lens.

The conditional expression (4) defines refractive power of the secondlens, and is a condition for shortening the total length and excellentlycorrecting the aberration. When the value is below the upper limit ofthe conditional expression (4), it becomes easy to make the total lengthshort while maintaining the refractive power of the second lens. On theother hand, when the value is above the lower limit of the conditionalexpression (4), it becomes easy to correct the spherical aberration andchromatic aberration occurred at the first lens.

According to the imaging lens having the above structure, it ispreferable that the third lens has positive refractive power.

By having the positive refractive power, the third lens makes the totallength shorter.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (5):

2.51<f3/f<16.53  (5)

wheref3: focal length of a third lens, andf: focal length of an overall optical system of an imaging lens.

The conditional expression (5) defines refractive power of the thirdlens, and is a condition for shortening the total length and excellentlycorrecting the aberration. When the value is below the upper limit ofthe conditional expression (5), it becomes easy to make the total lengthshort while maintaining the refractive power of the third lens. On theother hand, when the value is above the lower limit of the conditionalexpression (5), it becomes easy to suppress the high-order sphericalaberration and the coma aberration occurred at the third lens.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (6):

−1.83<f4/f<−0.81  (6)

wheref4: focal length of a fourth lens, andf: focal length of an overall optical system of an imaging lens.

The conditional expression (6) defines refractive power of the fourthlens. When the value is below the upper limit of the conditionalexpression (6), it becomes easy to correct distortion. On the otherhand, when the value is above the lower limit of the conditionalexpression (6), the total length can be shortened while maintaining backfocus.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (7):

1.68<f5/f<164  (7)

wheref5: focal length of a fifth lens, andf: focal length of an overall optical system of an imaging lens.

The conditional expression (7) defines refractive power of the fifthlens, and is a condition for shortening the total length and excellentlycorrecting the aberration. When the value is below the upper limit ofthe conditional expression (7), it becomes easy to make the total lengthshort while maintaining the refractive power of the fifth lens. On theother hand, when the value is above the lower limit of the conditionalexpression (7), the axial chromatic aberration occurred at the fifthlens becomes small and it becomes easy to correct the astigmatism.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (8):

−14.90<f345/f<−1.50  (8)

wheref345: composite focal length of a third lens, a fourth lens and a fifthlens, andf: focal length of an overall optical system of an imaging lens.

The conditional expression (8) defines refractive power of the compositefocal length of the third lens, the fourth lens and the fifth lens, andis a condition for shortening the total length and excellentlycorrecting the aberrations. When the value is below the upper limit ofthe conditional expression (8), it becomes easy to make the total lengthof the imaging lens short while maintaining negative refractive power ofthe third lens, the fourth lens and the fifth lens. On the other hand,when the value is above the lower limit of the conditional expression(8), it becomes easy to correct the field curvature and the chromaticaberration.

According to the imaging lens having the above structure, it ispreferable that the first lens has a convex surface facing the imageside near the optical axis.

By having the positive refractive power on the image-side surface, thefirst lens excellently corrects the spherical aberration.

According to the imaging lens having the above structure, it ispreferable that the second lens has biconcave shape near the opticalaxis.

By having the biconcave shape near the optical axis, the second lensincreases the negative refractive power and well corrects the comaaberration and the distortion.

According to the imaging lens having the above structure, it ispreferable that the fifth lens has a convex surface facing the imageside near the optical axis.

By making an image-side surface convex, the fifth lens guides theoff-axial light ray to the image plane while suppressing refractionangle at each surface to be small, and excellently corrects off-axialaberration.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (9):

24.85<νd1−νd2<46.15  (9)

whereνd1: abbe number at d-ray of a first lens, andνd2: abbe number at d-ray of a second lens.

The conditional expression (9) defines a scope of abbe numbers at d-rayof the first lens and the second lens, and is a condition forexcellently correcting the chromatic aberration. By using materialssatisfying the scope of the conditional expression (9), the chromaticaberration is excellently corrected and manufacturing cost is reduced.According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (10):

24.85<νd4−νd3<46.15  (10)

whereνd3: abbe number at d-ray of a third lens, andνd4: abbe number at d-ray of a fourth lens.

The conditional expression (10) defines a scope of abbe numbers at d-rayof the third lens and the fourth lens, and is a condition forexcellently correcting the chromatic aberration. By using materialssatisfying the scope of the conditional expression (10), the chromaticaberration is excellently corrected and manufacturing cost is reduced.

According to the imaging lens having the above structure, it ispreferable that at least one surface of each of the first lens, thesecond lens, the third lens, the fourth lens and the fifth lens is anaspheric surface.

Using the aspheric surface enables excellent correction of aberrations.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (11):

Fno≤2.5  (11)

where

Fno: F-number.

The conditional expression (11) defines the F-number, and satisfying theconditional expression (11) enables sufficient brightness to be ensuredwhen the imaging lens is mounted in the mobile terminal equipment and adigital camera.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (12):

−1.39<r3/r4<−0.62  (12)

wherer3: curvature radius of an object-side surface of a second lens, andr4: curvature radius of an image-side surface of a second lens.

The conditional expression (12) defines relationship of the curvatureradius of the object-side surface and the image-side surface of thesecond lens, and is a condition for effectively achieving reduction inmanufacturing error of the second lens while excellently correcting theaberration. When the conditional expression (12) is satisfied, theexcellent correction of the aberration is made while preventing therefractive power of the object-side surface and the image-side surfacefrom being excessive. Additionally, the conditional expression (12) isalso a condition for reducing the manufacturing error of the secondlens.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (13):

0.17<r5/r6<1.16  (13)

wherer5: curvature radius of an object-side surface of a third lens, andr6: curvature radius of an image-side surface of a third lens.

The conditional expression (13) defines relationship of the curvatureradius of the object-side surface and the image-side surface of thethird lens, and is a condition for preventing occurrence of theastigmatism. When the conditional expression (13) is satisfied, thethird lens has the meniscus shape near the optical axis and theastigmatism is properly corrected.

According to the imaging lens having the above structure, it ispreferable to satisfy a below conditional expression (14):

0.01<r7/r8<0.28  (14)

wherer7: curvature radius of an object-side surface of a fourth lens, andr8: curvature radius of an image-side surface of a fourth lens.

The conditional expression (14) defines relationship of the curvatureradius of the object-side surface and the image-side surface of thefourth lens, and is a condition for excellently correcting the sphericalaberration, shortening the total length and reducing sensitivity to themanufacturing error. When the value is below the upper limit of theconditional expression (14), it becomes easy to suppress the sphericalaberration occurred on this surface and reduce the sensitivity to themanufacturing error while maintaining the refractive power of theimage-side surface of the fourth lens. On the other hand, when the valueis above the lower limit of the conditional expression (14), thelow-profileness is realized while maintaining the refractive power ofthe fourth lens.

Effect of Invention

According to the present invention, there can be provided an imaginglens with high resolution which satisfies in well balancelow-profileness, low telephoto ratio and low F-number

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a general configuration of an imaginglens in Example 1 according to the present invention;

FIG. 2 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 1 according to the present invention;

FIG. 3 is a schematic view showing the general configuration of animaging lens in Example 2 according to the present invention;

FIG. 4 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 2 according to the present invention;

FIG. 5 is a schematic view showing the general configuration of animaging lens in Example 3 according to the present invention;

FIG. 6 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 3 according to the present invention;

FIG. 7 is a schematic view showing the general configuration of animaging lens in Example 4 according to the present invention; and

FIG. 8 shows spherical aberration, astigmatism, and distortion of theimaging lens in Example 4 according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the preferred embodiment of the present invention will bedescribed in detail referring to the accompanying drawings.

FIGS. 1, 3, 5 and 7 are schematic views showing the generalconfigurations of the imaging lenses in Examples 1 to 4 according to theembodiments of the present invention, respectively. Since all theseexamples have the same basic lens configuration, the generalconfiguration of an imaging lens according to this embodiment isexplained below mainly referring to the schematic view of Example 1.

As shown in FIG. 1, the imaging lens according to this embodimentcomprises, in order from an object side to an image side, a first lensL1, a second lens L2, a third lens L3, a forth lens L4 having a convexsurface facing an image side near an optical axis and a fifth lens L5having positive refractive power.

A filter IR such as an IR cut filter or a cover glass is located betweenthe fifth lens L5 and an image plane IMG (namely, the image plane of theimage sensor). The filter IR is omissible. The first lens L1 isconfigured to be a biconvex lens having convex surfaces facing theobject side and the image side near the optical axis. The second lens L2is a biconcave lens having concave surfaces facing the object side andthe image side near the optical axis. The third lens L3 has a meniscusshape having the convex surface facing the object side near the opticalaxis, and has positive refractive power. The fourth lens has a meniscusshape having the convex surface facing the image side near the opticalaxis, and has negative refractive power. The fifth lens L5 has ameniscus shape having the convex surface facing the image side near theoptical axis, and has positive refractive power.

The imaging lens according to the present embodiments facilitatesmanufacture by using plastic materials to all of the lenses, andrealizes mass production in a low cost. Both surfaces of all of thelenses are made as proper aspheric surfaces, and the aberrations arefavorably corrected.

The material adapted to the lens is not limited to the plastic material.By adapting glass material, further high performance may be aimed. Allof surfaces of lenses are preferably formed as aspheric surfaces,however, spherical surfaces may be adopted which is easy to manufacturein accordance with required performance.

The imaging lens according to the present embodiments shows preferableeffect by satisfying the below conditional expressions (1) to (14).

0.64<TTL/f<1.0  (1)

f<5.8  (2)

0.31<f1/f<0.63  (3)

−0.85<f2/f<−0.36  (4)

2.51<f3/f<16.53  (5)

−1.83<f4/f<−0.81  (6)

1.68<f5/f<164  (7)

−14.90<f345/f<−1.50  (8)

24.85<νd1−νd2<46.15  (9)

24.85<νd4−νd3<46.15  (10)

Fno≤2.5  (11)

−1.39<r3/r4<−0.62  (12)

0.17<r5/r6<1.16  (13)

0.01<r7/r8<0.28  (14)

Where

f: focal length of the overall imaging lens,TTL: distance along the optical axis from an object-side surface of thefirst lens L1 to an image plane,f1: focal length of the first lens L1,f2: focal length of the second lens L2,f3: focal length of the third lens L3,f4: focal length of the fourth lens L4,f5: focal length of the fifth lens L5,f345: composite focal length of the third lens L3, the fourth lens L4and the fifth lens L5,νd1: abbe number at d-ray of the first lens L1,νd2: abbe number at d-ray of the second lens L2,νd3: abbe number at d-ray of the third lens L3,νd4: abbe number at d-ray of the fourth lens L4,

Fno: F-number,

r3: curvature radius of the object-side surface of the second lens L2,r4: curvature radius of the image-side surface of the second lens L2,r5: curvature radius of the object-side surface of the third lens L3,r6: curvature radius of the image-side surface of the third lens L3,r7: curvature radius of the object-side surface of the fourth lens L4,andr8: curvature radius of the image-side surface of the fourth lens L4.

The imaging lens according to the present embodiments satisfies belowconditional expressions (1a), (3a) to (14a), and more preferable effectis realized:

0.73<TTL/f<1.0  (1a)

0.36<f1/f<0.58  (3a)

−0.79<f2/f<−0.42  (4a)

2.87<f3/f<15.26  (5a)

−1.69<f4/f<−0.92  (6a)

1.92<f5/f<152  (7a)

−13.76<f345/f<−1.71  (8a)

28.40<νd1−νd2<42.60  (9a)

28.40<νd4−νd3<42.60  (10a)

Fno≤2.4  (11a)

−1.29<r3/r4<−0.71  (12a)

0.20<r5/r6<1.07  (13a)

0.01<r7/r8<0.26  (14a)

where signs of each conditional expression are same as that in the lastparagraph.

Furthermore, the imaging lens according to the present embodimentssatisfies below conditional expressions (1b), (3b) to (14b), andparticularly preferable effect is realized:

0.82<TTL/f<1.0  (1b)

0.40<f1/f<0.53  (3b)

−0.72<f2/f<−0.47  (4b)

3.23<f3/f<13.99  (5b)

−1.55<f4/f<−1.04  (6b)

2.16<f5/f<139  (7b)

−12.61<f345/f<−1.93  (8b)

31.95<νd1−νd2<39.05  (9b)

31.95<νd4−νd3<39.05  (10b)

Fno≤2.3  (11b)

−1.18<r3/r4<−0.79  (12b)

0.22<r5/r6<0.98  (13b)

0.015<r7/r8<0.24  (14b)

where signs of each conditional expression are same as that in the lastparagraph.

In this embodiment, the aspheric shapes of the surfaces of the asphericlens are expressed by Equation 1, where Z denotes an axis in the opticalaxis direction, H denotes a height perpendicular to the optical axis, kdenotes a conic constant, and A4, A6, A8, A10, A12, A14, and A16 denoteaspheric surface coefficients.

$\begin{matrix}{Z = {\frac{\frac{H^{2}}{R}}{1 + \sqrt{1 - {\left( {k + 1} \right)\frac{H^{2}}{R^{2}}}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}} + {A_{12}H^{12}} + {A_{14}H^{14}} + {A_{16}H^{16}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Next, examples of the imaging lens according to this embodiment will beexplained. In each example, f denotes the focal length of the overalloptical system of the imaging lens, Fno denotes an F-number, ω denotes ahalf field of view, and ih denotes a maximum image height. Additionally,i denotes surface number counted from the object side, r denotes acurvature radius, d denotes the distance of lenses along the opticalaxis (surface distance), Nd denotes a refractive index at d-ray(reference wavelength), and νd denotes an abbe number at d-ray. As foraspheric surfaces, an asterisk (*) is added after surface number i.

Example 1

The basic lens data is shown below in Table 1.

Unit mm f = 5.68 Fno = 2.2 ω(°) = 21.8 ih = 2.30 TTL = 5.18 Surface DataSurface Curvature Surface Refractive Abbe Number i Radius r Distance dindex Nd Number νd (Object) Infinity Infinity  1 (Stop) Infinity −0.7967 2* 1.4102 1.0512 1.544 55.86 (νd1)  3* −57.4281 0.2587  4* −4.09860.2300 1.661 20.37 (νd2)  5* 4.2034 0.2376  6* 5.8539 0.2700 1.661 20.37(νd3)  7* 6.5491 1.0994  8* −3.5000 0.3250 1.544 55.86 (νd4)  9*−196.4474 0.1085 10* −94.9642 0.7195 1.661 20.37 (νd5) 11* −8.26100.1000 12 Infinity 0.2100 1.517 64.17 13 Infinity 0.6406 Image PlaneInfinity Constituent Lens Data Lens Start Surface Focal Length CompositeFocal Length 1 2 2.545 f345 −18.150 2 4 −3.106 3 6 72.285 4 8 −6.551 510  13.649 Aspheric Surface Data Second Surface Third Surface FourthSurface Fifth Surface Sixth Surface k 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00 0.000000E+00 A4 −1.407693E−03 8.992907E−023.109713E−01 2.229563E−01 −1.633799E−01 A6 −5.474899E−03 −3.751727E−02−4.340164E−01 −9.051976E−01 −4.141071E−01 A8 1.157969E−02 −1.783428E−024.098591E−01 4.865945E+00 3.028476E+00 A10 −1.021762E−02 3.702434E−02−2.346350E−01 −1.915265E+01 −1.151690E+01 A12 3.067386E−03 −1.337892E−022.750061E−01 4.445913E+01 2.479507E+01 A14 0.000000E+00 0.000000E+00−3.060518E−01 −5.293288E+01 −2.749487E+01 A16 0.000000E+00 0.000000E+001.200984E−01 2.560609E+01 1.237204E+01 Seventh Surface Eight SurfaceNinth Surface Tenth Surface Eleventh Surface k 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00 0.000000E+00 A4 −5.007662E−02 1.582924E−021.243904E−01 5.814651E−02 −4.340858E−02 A6 4.421675E−05 −1.193175E−01−2.014576E−01 −4.068109E−02 2.026847E−02 A8 4.734433E−01 1.467223E−011.218527E−01 −2.028018E−02 −6.462364E−03 A10 −1.395972E+00 −7.789333E−02−3.891744E−02 2.920151E−02 −1.961310E−03 A12 2.639468E+00 2.200898E−027.063018E−03 −1.174178E−02 1.919025E−03 A14 −2.568046E+00 −3.175992E−03−8.917631E−04 2.094079E−03 −4.487499E−04 A16 7.000000E−01 1.818016E−047.673108E−05 −1.419559E−04 3.529360E−05

The imaging lens in Example 1 satisfies conditional expressions (1) to(14) as shown in Table 5.

FIG. 2 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 1. The spherical aberration diagramshows the amount of aberration at wavelengths of F-ray (486 nm), d-ray(588 nm), and C-ray (656 nm). The astigmatism diagram shows the amountof aberration at d-ray on a sagittal image surface S and on tangentialimage surface T, respectively (same as FIG. 4, FIG. 6 and FIG. 8). Asshown in FIG. 2, each aberration is corrected excellently.

Example 2

The basic lens data is shown below in Table 2.

Example 2

Unit mm f = 5.40 Fno = 2.1 ω(°) = 22.8 ih = 2.30 TTL = 5.19 Surface DataSurface Curvature Surface Refractive Abbe Number i Radius r Distance dindex Nd Number νd (Object) Infinity Infinity  1 (Stop) Infinity −0.7500 2* 1.4429 1.0227 1.544 55.86 (νd1)  3* −70.9771 0.2606  4* −4.44840.2329 1.661 20.37 (νd2)  5* 5.0441 0.2447  6* 13.4574 0.3876 1.66120.37 (νd3)  7* 54.8964 0.8788  8* −3.2251 0.2941 1.544 55.86 (νd4)  9*−15.0431 0.0727 10* −55.7918 0.9964 1.661 20.37 (νd5) 11* −50.00000.1000 12 Infinity 0.2100 1.517 64.17 13 Infinity 0.5604 Image PlaneInfinity Constituent Lens Data Lens Start Surface Focal Length CompositeFocal Length 1 2 2.611 f345 −11.557 2 4 −3.543 3 6 26.881 4 8 −7.609 510  682.239 Aspheric Surface Data Second Surface Third Surface FourthSurface Fifth Surface Sixth Surface k 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00 0.000000E+00 A4 −3.212629E−03 6.519639E−022.437222E−01 1.968097E−01 −1.262989E−01 A6 1.399415E−03 −1.922983E−02−3.129261E−01 −8.486969E−01 −5.100122E−01 A8 3.036777E−04 −1.234310E−023.341045E−01 4.747900E+00 3.362740E+00 A10 −9.964776E−04 1.503697E−02−2.904179E−01 −1.773828E+01 −1.197436E+01 A12 3.116416E−04 −3.859927E−032.836570E−01 3.832227E+01 2.379143E+01 A14 0.000000E+00 0.000000E+00−1.924156E−01 −4.298765E+01 −2.445516E+01 A16 0.000000E+00 0.000000E+005.617813E−01 1.979820E+01 1.035410E+01 Seventh Surface Eight SurfaceNinth Surface Tenth Surface Eleventh Surface k 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00 0.000000E+00 A4 −6.531912E−02 2.073036E−039.767431E−02 2.676764E−02 −5.106757E−02 A6 −1.021886E−02 −1.614293E−01−2.019847E−01 −3.597268E−02 1.613648E−02 A8 4.883367E−01 1.810588E−011.222480E−01 −2.167341E−02 −3.388748E−03 A10 −1.781470E+00 −9.213830E−02−3.774958E−02 3.024803E−02 −2.054324E−03 A12 3.492610E+00 2.349837E−025.862099E−03 −1.238345E−02 1.286919E−03 A14 −3.150000E+00 −2.637752E−03−6.619518E−04 2.137989E−03 −2.617532E−04 A16 1.189007E+00 2.764803E−044.743618E−05 −1.326379E−04 1.855499E−05

The imaging lens in Example 2 satisfies conditional expressions (1) to(14) as shown in Table 5.

FIG. 4 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 2. As shown in FIG. 4, eachaberration is corrected excellently.

Example 3

The basic lens data is shown below in Table 3.

Example 3

Unit mm f = 5.72 Fno = 2.2 ω(°) = 21.7 ih = 2.30 TTL = 5.20 Surface DataSurface Curvature Surface Refractive Abbe Number i Radius r Distance dindex Nd Number νd (Object) Infinity Infinity  1 (Stop) Infinity −0.7950 2* 1.4107 1.0513 1.544 55.86 (νd1)  3* −71.7884 0.2596  4* −4.07490.2307 1.661 20.37 (νd2)  5* 4.2563 0.2369  6* 5.7204 0.2486 1.661 20.37(νd3)  7* 6.5110 1.0976  8* −3.5019 0.3610 1.544 55.86 (νd4)  9*−39.3996 0.1121 10* −27.6266 0.7087 1.661 20.37 (νd5) 11* −7.8418 0.100012 Infinity 0.2100 1.517 64.17 13 Infinity 0.6589 Image Plane InfinityConstituent Lens Data Lens Start Surface Focal Length Composite FocalLength 1 2 2.555 f345 −18.404 2 4 −3.116 3 6 63.371 4 8 −7.086 5 10 16.33910 Aspheric Surface Data Second Surface Third Surface FourthSurface Fifth Surface Sixth Surface k 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00 0.000000E+00 A4 −1.281886E−03 8.966316E−023.110655E−01 2.231940E−01 −1.634227E−01 A6 −5.413496E−03 −3.754461E−02−4.339445E−01 −9.052611E−01 −4.140807E−01 A8 1.159551E−02 −1.783811E−024.099225E−01 4.865994E+00 3.028126E+00 A10 −1.021650E−02 3.702686E−02−2.345778E−01 −1.915243E+01 −1.151734E+01 A12 3.065112E−03 −1.337761E−022.750695E−01 4.445959E+01 2.479519E+01 A14 0.000000E+00 0.000000E+00−3.059832E−01 −5.293218E+01 −2.749298E+01 A16 0.000000E+00 0.000000E+001.201907E−01 2.560692E+01 1.237773E+01 Seventh Surface Eight SurfaceNinth Surface Tenth Surface Eleventh Surface k 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00 0.000000E+00 A4 −4.991616E−02 1.617039E−021.246625E−01 5.786059E−02 −4.315439E−02 A6 3.506411E−04 −1.193104E−01−2.017638E−01 −4.064162E−02 2.024934E−02 A8 4.740283E−01 1.467208E−011.218299E−01 −2.027872E−02 −6.464286E−03 A10 −1.395365E+00 −7.789456E−02−3.891867E−02 2.920124E−02 −1.961362E−03 A12 2.640006E+00 2.200851E−027.063161E−03 −1.174190E−02 1.919056E−03 A14 −2.461000E+00 −3.176141E−03−8.916633E−04 2.094047E−03 −4.487379E−04 A16 9.565873E−01 1.817583E−047.676139E−05 −1.419642E−04 3.529453E−05

The imaging lens in Example 3 satisfies conditional expressions (1) to(14) as shown in Table 5.

FIG. 6 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 3. As shown in FIG. 6, eachaberration is corrected excellently.

Example 4

The basic lens data is shown below in Table 4.

Example 4

Unit mm f = 5.54 Fno = 2.2 ω(°) = 22.3 ih = 2.30 TTL = 5.12 Surface DataSurface Curvature Surface Refractive Abbe Number i Radius r Distance dindex Nd Number νd (Object) Infinity Infinity  1 (Stop) Infinity −0.7950 2* 1.4113 1.0527 1.544 55.86 (νd1)  3* −64.2650 0.2628  4* −3.99410.2225 1.661 20.37 (νd2)  5* 3.7286 0.2182  6* 5.4480 0.2577 1.661 20.37(νd3)  7* 9.1432 1.1014  8* −3.5669 0.3305 1.544 55.86 (νd4)  9*−54.1212 0.1004 10* −52.2408 0.6653 1.661 20.37 (νd5) 11* −8.4265 0.100012 Infinity 0.2100 1.517 64.17 13 Infinity 0.6707 Image Plane InfinityConstituent Lens Data Lens Start Surface Focal Length Composite FocalLength 1 2 2.551 f345 −63.490 2 4 −2.885 3 6 19.851 4 8 −7.032 5 10 15.114 Aspheric Surface Data Second Surface Third Surface Fourth SurfaceFifth Surface Sixth Surface k 0.000000E+00 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00 A4 −1.430144E−03 8.924638E−02 3.116414E−012.221285E−01 −1.610874E−01 A6 −5.385009E−03 −3.766936E−02 −4.334775E−01−9.047098E−01 −4.166531E−01 A8 1.170417E−02 −1.790720E−02 4.098565E−014.861380E+00 3.021672E+00 A10 −1.018934E−02 3.700499E−02 −2.358896E−01−1.916294E+01 −1.152600E+01 A12 3.000705E−03 −1.340532E−02 2.729725E−014.444948E+01 2.479192E+01 A14 0.000000E+00 0.000000E+00 −3.069008E−01−5.292252E+01 −2.747868E+01 A16 0.000000E+00 0.000000E+00 1.232619E−012.568024E+01 1.241259E+01 Seventh Surface Eight Surface Ninth SurfaceTenth Surface Eleventh Surface k 0.000000E+00 0.000000E+00 0.000000E+000.000000E+00 0.000000E+00 A4 −5.299219E−02 1.603897E−02 1.258225E−015.691534E−02 −4.341982E−02 A6 6.263363E−04 −1.192005E−01 −2.019386E−01−4.074627E−02 2.009667E−02 A8 4.710055E−01 1.467499E−01 1.218660E−01−2.030598E−02 −6.464951E−03 A10 −1.396879E+00 −7.789109E−02−3.890232E−02 2.919646E−02 −1.960265E−03 A12 2.637947E+00 2.200849E−027.068080E−03 −1.174250E−02 1.918933E−03 A14 −2.530000E+00 −3.176635E−03−8.902697E−04 2.094071E−03 −4.488955E−04 A16 9.621729E−01 1.814586E−047.714677E−05 −1.419205E−04 3.522503E−05

The imaging lens in Example 4 satisfies conditional expressions (1) to(14) as shown in Table 5.

FIG. 8 shows spherical aberration (mm), astigmatism (mm), and distortion(%) of the imaging lens in Example 4. As shown in FIG. 8, eachaberration is corrected excellently.

In table 5, values of conditional expressions (1) to (14) related to theExamples 1 to 4 are shown.

Conditional Expression Example 1 Example 2 Example 3 Example 4 (1) T TL/f 0.91 0.96 0.91 0.92 (2) f 5.68 5.40 5.72 5.54 (3) f 1/f 0.45 0.480.45 0.46 (4) f 2/f −0.55 −0.66 −0.54 −0.52 (5) f 3/f 12.72 4.98 11.073.58 (6) f 4/f −1.15 −1.41 −1.24 −1.27 (7) f 5/f 2.40 126.29 2.86 2.73(8) f 3 4 5/f −3.19 −2.14 −3.22 −11.46 (9) v d 1 − v d 2 35.50 35.5035.50 35.50 (10)  v d 4 − v d 3 35.50 35.50 35.50 35.50 (11)  F n o 2.212.09 2.23 2.15 (12)  r 3/r 4 −0.98 −0.88 −0.96 −1.07 (13)  r 5/r 6 0.890.25 0.88 0.60 (14)  r 7/r 8 0.02 0.21 0.09 0.07

When the imaging lens comprising five lenses according to the presentinvention is adapted to an imaging device mounted in an increasinglylow-profile and low F-number smartphone and mobile terminal equipment,an information equipment such as a game console, PC and a robot, andmoreover, a home appliance and an automobile with camera function, thereis realized low-profileness, reduction in telephoto ratio andcontribution to low F-number of the camera, and also high performancethereof.

DESCRIPTION OF REFERENCE NUMERALS

-   ST: aperture stop,-   L1: first lens,-   L2: second lens,-   L3: third lens,-   L4: fourth lens,-   L5: fifth lens,-   ih: maximum image height,-   IR: filter, and-   IMG: image plane

What is claimed is:
 1. An imaging lens comprising in order from an object side to an image side, a first lens, a second lens, a third lens, a fourth lens having a convex surface facing the image side near an optical axis, and a fifth lens having positive refractive power, wherein a below conditional expression (1) is satisfied: 0.64<TTL/f<1.0  (1) where f: focal length of an overall optical system of an imaging lens, and TTL: distance along the optical axis from an object-side surface of the first lens to an image plane.
 2. The imaging lens according to claim 1, wherein a conditional expression (2) below is satisfied: f<5.8  (2) where f: focal length of the overall optical system of the imaging lens.
 3. The imaging lens according to claim 1, wherein a conditional expression (3) below is satisfied: 0.31<f1/f<0.63  (3) where f1: focal length of the first lens, and f: focal length of the overall optical system of the imaging lens.
 4. The imaging lens according to claim 1, wherein a conditional expression (4) below is satisfied: −0.85<f2/f<−0.36  (4) where f: focal length of the overall optical system of the imaging lens, and f2: focal length of the second lens.
 5. The imaging lens according to claim 1, wherein the third lens has positive refractive power.
 6. The imaging lens according to claim 1, wherein a conditional expression (5) below is satisfied: 2.51<f3/f<16.53  (5) where f: focal length of the overall optical system of the imaging lens, and f3: focal length of the third lens.
 7. The imaging lens according to claim 1, wherein a conditional expression (6) below is satisfied: −1.83<f4/f<−0.81  (6) where f: focal length of the overall optical system of the imaging lens, and f4: focal length of the fourth lens.
 8. The imaging lens according to claim 1, wherein a conditional expression (7) below is satisfied: 1.68<f5/f<164  (7) where f: focal length of the overall optical system of the imaging lens, and f5: focal length of the fifth lens.
 9. The imaging lens according to claim 1, wherein a conditional expression (8) below is satisfied: −14.90<f345/f<−1.50  (8) where f: focal length of the overall optical system of the imaging lens, and f345: composite focal length of the third lens, the fourth lens and the fifth lens.
 10. The imaging lens according to claim 1, wherein said first lens has a convex surface facing the image side near the optical axis.
 11. The imaging lens according to claim 1, wherein said second lens has biconcave shape near the optical axis.
 12. The imaging lens according to claim 1, wherein said fifth lens has a convex surface facing the image side near the optical axis.
 13. The imaging lens according to claim 1, wherein a conditional expression (9) below is satisfied: 24.85<νd1−νd2<46.15  (9) where νd1: abbe number at d-ray of the first lens, and νd2: abbe number at d-ray of the second lens.
 14. The imaging lens according to claim 1, wherein a conditional expression (10) below is satisfied: 24.85<νd4−νd3<46.15  (10) where νd3: abbe number at d-ray of the third lens, and νd4: abbe number at d-ray of the fourth lens.
 15. The imaging lens according to claim 1, wherein at least one surface of each of said first lens, said second lens, said third lens, said fourth lens and said fifth lens is an aspheric surface.
 16. The imaging lens according to claim 1, wherein a conditional expression (11) below is satisfied: Fno≤2.5  (11) where Fno: F-number.
 17. The imaging lens according to claim 1, wherein a conditional expression (12) below is satisfied: −1.39<r3/r4<−0.62  (12) where r3: curvature radius of the object-side surface of the second lens, and r4: curvature radius of the image-side surface of the second lens.
 18. The imaging lens according to claim 1, wherein a conditional expression (13) below is satisfied: 0.17<r5/r6<1.16  (13) where r5: curvature radius of the object-side surface of the third lens, and r6: curvature radius of the image-side surface of the third lens.
 19. The imaging lens according to claim 1, wherein a conditional expression (14) below is satisfied: 0.01<r7/r8<0.28  (14) where r7: curvature radius of the object-side surface of the fourth lens, and r8: curvature radius of the image-side surface of the fourth lens. 